1. Technical Field
The technical field relates to directional acoustic systems and more particularly to a blended folded waveguide/horn and acoustic reflector.
2. Description of the Technical Field
The reproduction of sound with high fidelity and at high intensity levels across a broad frequency range, poses a number of challenges. To do so from a small, energy-efficient package, portable enough to be moved and suitable for open air use is especially difficult. The issues are compounded where it is desirable to build a device based on a single transducer which can cover most of the audible frequency spectrum. Generally, high output, high efficiency loudspeaker systems have been built around horns. Low frequency units use propagation paths of relatively long lengths. In order to reduce external package size low frequency horns have had folded axes. The greater the degree of folding the more compact a horn can be made at the cost of restricting throughput of higher acoustic frequencies.
Klipsch, in U.S. Pat. No. 4,138,594, taught a small dimension low frequency loudspeaker incorporating a folded or “reflexed” horn which could operate in conjunction with mid and high range loudspeakers. The mid to high range loudspeakers were horn loaded using straight axis horns to produce a broad spectrum system. The Klipsch low frequency subsystem reflected research that found that a low frequency horn could be built using approximations of an exponential flare rather than a true curved interior surface. This allowed Klipsch to introduce flat surfaces to the low frequency horn, simplifying construction, and with minimal distortion for sounds at frequencies below 300 Hz.
Loudspeakers loaded with folded axis horns have not been favored for sound frequencies above about 300 Hz, particularly in the mid and upper ranges of human hearing. Klipsch found that folding produced severe variations in amplitude response of the horn. Folding a horn introduces an upper cut off frequency for sound transmission through the horn due to the fold giving rise to a standing wave in the horn above that frequency preventing emission of higher frequency sound from the horn. The cut off frequency, and the sharpness of sound transmission fall off, is a function of the degree of the angle subtended by the fold, how tight the angle is, and the cross sectional area of the horn in the vicinity of the fold. The flat faces in the Klipsch folded low frequency horn produce sharp turns in the horn which, while insignificant at low frequencies, but which came into play at higher frequencies. As a consequence Klipsch provided that the mid and upper frequency range loudspeakers were loaded with straight axis horns and the folded horn was restricted to use with a low frequency transducer.
Straight “multiple entry” horns are known which combine transducers in different band passes in a single horn.